The present invention relates to an antenna duplexer used in mobile communication appliances, and more particularly to a multi-frequency antenna duplexer.
A conventional antenna duplexer is generally formed of coaxial resonators or distributed constant type resonators, and the number of stages of resonators and their shape are determined in order to obtain desired electric characteristics such as passing band width and attenuation amount.
A conventional multi-frequency antenna duplexer includes, as shown in FIG. 13, plural antenna duplexers, that is, transmitter filters 25a, 25b and receiver filters 26a, 26b respectivelly formed of coaxial resonators on a substrate 24. A switchable time division multiple access (TDMA) system contains, as shown in FIG. 14, a branching filter 23 for branching the passing frequency, and single pole double throw (SPDT) switches 27a, 27b for changing over transmission and reception. The SPDT switches 27a, 27b respectively change over transmitter terminals 16c, 16d, and receiver terminals 17c, 17d. 
In this multi-frequency antenna duplexer, it is hard to reduce in size because the filter characteristic depends largely on the shape of resonators. In particular, a non-switchable code division multiple access (CDMA) system requires multiple resonators, and is increased in size. For example, when an multi-frequency antenna duplexer largely different in passing band frequency such as 800 MHz and 1.8 GHz is composed of distributed constant type resonators, the electric characteristic of substrate materials used in the distributed constant type resonators depends on the frequency. Therefore, it is hard to optimize the electric characteristic of substrate materials.
A small-sized multi-frequency antenna duplexer is presented. The antenna duplexer uses plural antenna duplexers, each of which includes two surface acoustic wave filters each for transmitter and receiver having passing bands different in frequency from each other, attenuating other""s passing band each other. This multi-frequency antenna duplexer contains plural antenna duplexers mounted in one package. Further the passing band of each antenna duplexer is different from those of other antennas.
Thus, the multi-frequency antenna duplexer is reduced in size.
In this multi-frequency antenna duplexer, a first piezoelectric substrate on which plural transmitter surface acoustic wave filters are formed, a second piezoelectric substrate on which plural receiver surface acoustic wave filters are formed, and a phase shift substrate having a function of rotating the phase of each transmission band at least in each receiver surface acoustic wave filter are mounted in one package. Thus, the multi-frequency antenna duplexer suppresses signal leak between transmission and reception portions, and is reduced in size while maintaining isolation.
Further, in this multi-frequency antenna duplexer, transmitter surface acoustic wave filters and receiver surface acoustic wave filters, which constitute the antenna duplexer having passing bands different in frequency, are formed individually on one piezoelectric substrate. Further in each receiver surface acoustic wave filter, phase shift substrate having a function of rotating the phase of each transmission band are configured and mounted in a three-dimensional structure in one package. Thus, in this multi-frequency antenna duplexer, plural antenna duplexers, having passing bands largely different in frequency from each other, can be reduced in size without deteriorating the characteristics.
Herein, in the multi-frequency antenna duplexer, as for the antenna duplexer for two frequencies corresponding to two passing band frequencies, only one antenna output terminal may be required by connecting a branching filter installed in the one package as the antenna duplexer to the antenna terminal of each antenna duplexer. As a result, a small-sized multi-frequency antenna duplexer may be obtained.
Further, by forming the phase shift substrate and branching filter used in the multi-frequency antenna duplexer in the package inner layer, an multi-frequency antenna duplexer of further smaller size is obtained.
Moreover, in the multi-frequency antenna duplexer, by using the surface acoustic wave filters and bulk wave filters selectively depending on the passing band frequency or desired filter characteristic, an antenna duplexer for plural frequency having a superior performance can be realized in a smaller size.